1. Field of the Invention
This invention generally relates to integrated circuits and more specifically to devices for the storage and transport of such integrated circuits characterized by solder ball terminals.
2. Description of Related Art
The storage and transportation of semiconductor components have become important considerations in the production of electronic assemblies, especially as semiconductor components have matured from inexpensive, elementary circuit elements into expensive, sophisticated, complex circuit components. As these components have grown in complexity, they have become more susceptible to damage from a number of external influences, such as mechanical shock and discharges of accumulated electrostatic charge. Consequently, there have been many changes in the transportation, assembly and testing procedures that electronic assembly production facilities utilize. Such procedures, when properly implemented, now contribute significantly to the success of such electronic assembly facilities.
For example, in certain circumstances it is important to transport a component, such as an integrated circuit, pretest it, and provide ready access to the component for delivery to or insertion into a printed circuit board. "Chip carriers" provide such functions for individual components. "Chip carriers" are special fixtures that house and protect individual components, such as an integrated circuits, from damage due to mechanical shock or electrostatic discharge during processing, production, testing and assembly operations. A chip carrier also can orient an integrated circuit during the production process, assure proper placement and alignment of terminals for testing and for insertion into a printed circuit board.
In other circumstances, there may only be a requirement for the storage and shipment of large numbers of integrated circuits and like components without testing. For example, integrated circuit manufacturers ship such components to customers in bulk quantities. Some customers may desire to move such components in groups or sets directly to a printed circuit board. Other customers may desire to transport or store such components and then transfer the components to chip carriers or the like for further transportation and testing. When this limited requirement exists, it is difficult to justify the costs of purchasing and handling individual chip carriers. Examples of devices that store or carry multiple semiconductor components on a simple device are illustrated in the following U.S. Pat. Nos.:
3,469,686 (1969) Gutsche et al. PA1 3,482,682 (1969) Cronkhite PA1 3,361,253 (1972) Cronkhite PA1 3,946,864 (1976) Hutson PA1 4,057,142 (1977) Lechner et al. PA1 4,210,243 (1980) McDowell PA1 4,725,918 (1988) Bakker PA1 4,792,042 (1988) Koehn et al. PA1 5,103,976 (1992) Murphy
The foregoing references disclose generally devices for storing semiconductor wafers. Such wafers, however, do not have terminals that are normally encountered in finished integrated circuits. These trays are not readily adapted to devices with terminals. However, the following United States Letters Patent disclose devices for the shipment and transportation of integrated circuit components or for circuits utilizing such integrated circuit components:
U.S. Pat. No. 4,210,243 to McDowell discloses a tray for holding integrated circuit packages of the transistor outline type. This tray has a top plate with a plurality of funnel shaped openings each having a cylindrical bottom portion for receiving a case. The top and bottom edges of the trays are dimensioned so that the top of a first tray nests inside the bottom of a second tray. When the nested trays are turned over, packages and openings in the first tray sit with the flat portions of their leads on the bottom of the second tray. A rim limits transverse movement of the packages set on the plate when the tray is shaken to cause them to fall into associated openings.
U.S. Pat. No. 4,725,918 to Bakker discloses a box for storing electronic devices apparently including integrated circuits. The box includes a material that minimizes electrostatic accumulation and resultant discharges that could otherwise damage the electronic device.
U.S. Pat. No. 4,792,042 to Koehn et al. discloses a chip carrier for individual electronic circuits. It is possible to stack these chip carriers for shipment in bulk, albeit, in a single package.
Each of the foregoing McDowell, Bakker and Koehn et al. patents describes a device for use with a component of a single size or limited range of sizes. The Murphy patent discloses a tray for the transportation and storage of pin grid array integrated circuit components. A pin grid array (PGA) integrated circuit component typically has a thin planar housing of a ceramic or other material for containing a semiconductor substrate and related circuitry. Terminal pins extend perpendicularly to one planar surface of the housing. The terminal pins define an array or matrix of columns and rows with an industry-standard spacing. Currently the spacing is 0.1 inch so the terminal density is about 100 terminals per square inch. PGA integrated circuit components come in myriad sizes that are defined alternatively by the size of the housing (from a 1 inch square to a 2.5 inch square) or by the size of the matrix (from a 9.times.9 terminal pin matrix to a 25.times.25 terminal pin matrix).
The Murphy patent discloses stackable trays for carrying multiple PGA integrated circuit components. Each tray has a lattice framework that defines discrete storage pocket areas. Each storage pocket area comprises a base support that spans portions of the framework and includes upstanding ribs that engage the integrated circuit component. The locus of the upstanding ribs of a given set constitutes a rectangle or square that is concentric with and spaced from the locus of other sets of upstanding ribs. Depending terminal pins from the housing lie between individual ones of the upstanding ribs.
These trays have proven to accommodate various characteristics inherent in such components and to satisfy other requirements imposed by manufacturing processes. For example, this tray provides a direct, repeatable correlation between the tray and the terminal pins. It also protects the terminal pins from damage due to mechanical shock during transport and prevents the accumulation of an electrostatic charge on the PGA integrated circuit component to avoid a potential discharge and damage.
Integrated circuit manufacturers now produce an integrated circuit package called a ball grid array (BGA) integrated circuit. BGA integrated circuits are characterized by a thin planar housing and a plurality of external terminals on one side of that housing. Each external terminal comprises a small solder ball. Like prior art PGA integrated circuit packages, the solder ball terminals in a BGA integrated circuit package can be arranged in a two-dimensional array. However, the terminal density in a BGA integrated circuit package is many times (up to 7 or more times) greater than attained with PGA integrated circuit packages.
The manufacturers of BGA integrated circuit packages and their customers who assemble these packages onto circuit boards have evolved a series of handling requirements that are more restrictive than those associated with PGA integrated circuit packages. For example, solder ball terminals are more susceptible to physical damage than the terminal pins in PGA integrated circuit packages. Consequently both manufacturers and customers want a common component tray that protects the integrated circuit from physical and electrical damage. Both want a tray that provides repeatable positioning of the BGA integrated circuit package in the tray to enhance automated assembly techniques. Both want a tray that will store multiple BGA integrated circuit packages and that will stack with other trays to facilitate bulk transport and storage.
However, the manufacturers and customers have a set of apparently antithetical requirements that must be met without sacrificing any of the common requirements. Specifically, manufacturers want to transport BGA integrated circuit packages in a "terminals up" configuration in which the planar housing is substantially horizontal and the solder ball terminals are "on top" of the housing. This "terminals up" position facilitates the inspection and testing of the BGA integrated circuit package by the manufacturer prior to shipment. Moreover, some customers will desire to work with the components in this "terminals up" orientation for initial inspection and preliminary testing. However, most users will want to "flip" the component to a "terminals down" position for robitics to pick and place when being joined to a circuit board. In a "terminals down" position the planar housing is essentially horizontal and the terminals are on the "bottom" of the planar housing.
None of the prior art storage trays is capable of providing all these requirements. In each it would be necessary to design separate trays for each of the "terminals up" and "terminals down" orientations and to establish some methodology for transferring the BGA integrated circuit packages individually in one orientation in one tray to the second orientation in the other tray. Such a methodology is not be acceptable because it introduces extra manufacturing time and costs and because any such handling introduces an increased risk of integrated circuit component damage.